I agree they'll walk it back as soon as it makes sense to do so, but not because they don't want to call a Biden win... but because it's their chance to get back on the fence in general, which is where any news organization should be at this stage. Overall, they have been calling states for Biden (and Trump) much sooner than most of the other news organizations, so they haven't shown any reluctance to calling it the way they see it. I wouldn't be surprised if they call a Biden win first -- it seems like they want to be breaking these calls and getting the traffic/views.
Brian Stelter (CNN Chief Media Correspondent/Anchor of Reliable Sources) said on Monday night that although the Fox Editorial department is a dumpster fire (not his exact words), the AP/Fox election desk is trustworthy and usually does a trustworthy job (it's not just Fox News alone, they're working alongside the AP).
I've been flipping through the networks and other than Fox News calling Arizona a little before they probably should have, they haven't shown any bias toward either candidate in the numbers. I can't say the same for the guests they have chosen to have on.
I bet Fox just holds back on calling NV for Biden (no need if something radical happens and it can be called for Trump) until both NV and either AZ is certain (and can either also be called for Biden or flipped for Trump without going in to an indeterminant state) or one of GA or PA (for Biden) is clear and can be safely called as well.
I also think other orgs are probably holding back on calling NV because AP and Fox have called AZ, and there is a psychological effe t of having major orgs having called 270 EVs when overlayed, even if no one org has called 270.
Twitter’s rule-of-two on election results may play a role here, too.
tl;dr is that many of the remaining votes are in parts of the state that are more liberal than the parts of the state that have already been counted. If Biden wins a county that is 50/50 D/R, then they're assuming that he will also win a county that is 60/40 D/R (oversimplifying a bit because turnout can very from county to county and mail-in ballots might have different demographics than in person voters). However it was a bit controversial that Fox called AZ as early as they did, I don't think any of the other TV channels have followed suit
Networks will attempt to project ("call") winners based on how the data is trending. It has nothing to do with the official results. For instance, I understand that Fox "called" Arizona for Biden already, but I know that CNN and ABC have not.
https://www.nytimes.com/interactive/2020/11/03/upshot/networ...